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I have decided to secure additional wood members to each side of my keelson to address the end decay on the frames/ribs.
What are some techniques for determining the angle at each frame in order to transfer it to my material prior to cutting and planning?
I've thought about cutting individual blocks with a miter box until I match each frame to keelson angle. Using the blocks to take-off the angle as I plane down the new piece.
See additional posting on keelson condition.

Just looked at boat and thought the sister keelsons could be used as patterns for the additional members at the sides of keelson.

Excellent idea! JoeCB sent me the angle templates from his '57 Lancer for use on my keelson replacement, but you've apparently hit upon the obscure, obvious answer to determining those angles. Get a cheap angle gauge (Harbor Freight $5 or so, probably similar$$ at HD/Lowe's) and take off the angle from there. Simple!

-wte

PS - Happy birthday tomorrow!

I just went out and looked at the remnants of the keelson sisters (the pieces that are screwed onto the sides of the keelson) and it does not appear that their bottom edge is mitered to match the angle of the bottom planks... the edges appear square. From a production perspective I would not expect that the factory would invest the effort to fair this tiny surface.
I suggest that you will get the best measure of the hull angle at the keel by using an angle gage or making trial and error cardboard templates from the fair (not hogged) garboard planks. Absent this fair condition, you could interpolate the angle change from the near flat at the transom to what , hopfully would be a true angle up near the forward end of the keelson.

Joe C B

Joe,

I think Woody's referring to the "sister keelsons" AKA the "stringers", but by the Thompson terminology. Those members are definitely beveled to a changing angle.

Having taken the bottom off one side of my Sea Lancer now, the keelson "cheeks" (not Thompson terminology) do appear to be beveled as well. These are the pieces that the rib/frame tails land on. If, as we discussed in one of my earlier threads, the frames take a straight line from the turn of the bilge to the keelson, then the sister keelsons will have the same bevel angle as the "cheeks" of the keelson. In my boat's case, the sister keelsons appear to be in much better shape than the keel & keelson, probably due to their higher elevation and thus less time sitting in bilge water over the years.

-wte

It has always been my opinion that the construction of the keelson, keelson sisters (cheeks) and rib ends was a weak point in the Thompson design. The unsealed joint between the cheeks and the keelson retains moisture and breeds rot. The unsealed butt ends of the ribs wick up water and the fact that each rib end is punctured by two fasteners just aggrevates the problem.
Joe B